In disk-type magnetic recording systems for digital applications, magnetic transducer elements, or heads, are used to record information onto (i.e., write) or retrieve information from (i.e., read) the disk surface or surfaces. Each storage disk comprises an annular substrate onto which is deposited a magnetic recording medium. Each disk surface is divided into several concentric, annular bands, or "tracks" each having a predetermined radial extent. Adjacent tracks are separated by an unused buffer zone. Each head is supported in close proximity to an associated disk surface by a head positioning assembly, or actuator, that supports the head near the disk surface and moves it from one radial position to another, thereby permitting use of a single head for reading and writing on multiple tracks. The positioner assembly for each head or group of heads includes an actuator arm and an actuator motor. The actuator motor moves the actuator arm, to change the position of the head with relation to the tracks on the disk. A disk drive may include a plurality of stacked disks, and one actuator motor may be used to move a corresponding number of actuator arms in unison.
In particular, positioner assemblies of the prior art typically consist of several arms, in spaced apart relationship, stacked one above the other, pivoted at their centers on a common pivot, with read/write heads mounted at one end and the moving winding(s) of the rotor of the actuator motor mounted at the other. The stator portion of the motor includes permanent magnets and a flux conductive member that form a closed flux conductive path for the actuator motor. The winding thus also acts as a counterweight to balance the heads.
During operation, the positioner assembly provides high speed disk file access by positioning the read/write heads in a transducing relationship with a rotating magnetic storage disk. Such operation requires, first, that the position of the read/write head relative to a track on the disk be maintained within extremely close tolerances; and, second, that the access time (that is, the time required to move the head from one track to another desired track) be short. The state of the art concerning the first requirement necessitates that a control system, preferably utilizing feedback, be employed to sense the deviation of the position of the head from an optimum read/write position over the track, and to generate a correction signal for driving the actuator motor. A short access time, on the other hand, requires a number of different considerations such as the moving mass and inertia of the positioner and heads. The access time is further affected by the torque generated from the actuator motor that is ultimately transposed on to the positioner assembly.
One alternative for minimizing disk file access time is to increase the torque vector of the actuator motor for increasing the acceleration and deceleration of the positioner assembly. However, in order to increase the torque vector of an actuator motor, a proportional increase in overall motor size is required. Another alternative for increasing the acceleration and deceleration of the positioner assembly is to increase the magnitude of the current profiles supplied to the actuator motor windings. Both of the above described methods increase the acceleration and deceleration of the positioner assembly, however, either method causes an undesirable increase in power consumption. Furthermore, the former method, i.e., an increase in actuator motor size, undesirably requires additional physical space within the disk drive system.
It has been realized that typical disk drive systems write or read data to or from a disk storage surface starting from the outer diameter tracks and progressively write or read inwardly towards the inner diameter tracks. The reasoning for such formatting is that a greater number of data bits may be stored at the outer diameter tracks than at the inner diameter tracks, thereby minimizing the need to radially move the read/write head to subsequent data tracks. Minimizing radial movement of the read/write head increases data transfer rates and generally improves performance of the disk drive system. Typically, the majority of the unused portion of the disk drive system is located at the inner diameter track region of the storage disk. Thus, the desire for minimizing average disk file access may be accomplished by increasing the actuator torque vector when the actuator motor is positioning the read/write heads at the outer diameter tracks while maintaining the access time to inner diameter tracks virtually unchanged.
Thus, a hitherto unsolved need has remained for an actuator motor that will reduce average access time to a disk file storage system by increasing the actuator motor torque vector when accessing outer diameter tracks while maintaining the access time to inner diameter tracks virtually unchanged. Moreover, an unsolved need has remained for an actuator motor that provides minimized average access time to a disk file storage system with no appreciable increase in power consumption.